Recently, the wiring width and thickness of the semiconductor device have been decreased according to the increase of the density of integration in the semiconductor device. Here, a problem is encountered that the reliability of the wiring is decreased by the failure of the wiring made of aluminum due to electromigration or stress migration.
To improve the reliability of aluminum, a technique has been proposed which makes the size of grains of the grains of aluminum larger and improves the direction of the aluminum crystal so as to tolerate the electromigration and stress migration (Junichi Wada, et al., "New Method of Making Al single crystal interconnections on amorphous insulator", published in International Reliability Physics Symposium(IRPS)).
In this method the Al single crystal is used to form the wiring to tolerate the electromigration and stress migration.
FIGS. 1(a) to 1(c) illustrate the prior art fabrication process. As shown in FIG. 1(a), an oxide film 2 having a thickness of 1 .mu.m is formed on a silicon substrate 1 having a (100) direction and grooves 3 are formed in the oxide film 2 at regular-intervals by using Reactive Ion Etching (RIE) method. Here, the grooves 3 have a depth of 0.4 .mu.m, a width of 0.6 .mu.m and a pitch of 0.6 .mu.m.
Aluminum film 4 having a thickness of 0.4 .mu.m is deposited on the whole surface by using DC (direct current) magnetron sputtering under the normal temperatures as shown in FIG. 1(b).
And, an in-situ heat treatment 5 is performed from bottom of the substrate i by using a halogen lamp heater where the temperature is set at 500 degrees C. and the time at 45 seconds under Ar gas, as shown in FIG. 1(c)(Here, the in-situ heat treatment means that a constant heat treatment is performed, for depositing the aluminum film, in a vacuum in the sputtering chamber which is not broken, so that an oxide film is not formed on the aluminum wiring film.). Thereafter, the aluminum wiring film is patterned to a desired form to complete the wiring process.
As a result of forming the aluminum wiring film in the above processes, the aluminum wiring film filled in the grooves 3 is converted to the single crystal with the same orientation.
Accordingly, the single crystal aluminum having a high tolerance against electromigration and stress migration can improve the reliability of the semiconductor device.
However, in the above technique, stability is degraded when the grooves are formed in the oxide film because the depth of the grooves are controlled by the etching time of the RIE method. Thus, there is a problem that a step coverage of aluminum filled in the grooves is degraded when the aluminum film is deposited by using the sputtering method, so that a uniform single crystal of aluminum can not be obtained on the following process of the heat treatment. Also, there has been a problem in the reproduction due to the development of the slope of temperature around the grooves.